Tool life is determined by the tool's resistance to several types of wear and its response to heavy loads and to shock, with the reality that wear resistance is generally increased at the expense of strength. Today, the best tools exhibit the best compromises, and therefore are limited to use in special applications. To limit such compromises, coating techniques have been used to permit not only longer tool life but also increased cutting speeds and feeds. Powder metallurgy and sintering have lead to the development of new materials with enhanced hardness and toughness. Adding a hard coating to the sintered alloy such as by chemical vapor deposition (CVD), physical vapor deposition (PVD), or plasma-assisted chemical vapor deposition (PACVD) has increased wear resistance.
Mechanical properties have been improved by various engineering modifications, including lamination, part geometry, and by additional mechanical and/or thermal processes to enhance localized wear resistance. However, these additional processes add cost and lead times and often require more process steps such as brazing, forging, heat treatment, grinding, or lapping.
The external coating solution has several major disadvantages, including coating delamination and cracking in use (from different coating and substrate thermal expansion rates and from bending and surface loads) and the high CVD process temperatures required (900° C.-1200° C.) may not be consistent with the heat-treatment needed for the strength or the geometry of the sintered part.
Moreover, even with the use of high performance coatings on the surface of tools, the coatings eventually fail, and as the properties of the underlying material are insufficient to operate at cutting speeds the tool fails very quickly. While such tools could be rejuvenated by reapplying a CVD coating, the reapplication of a coating or multiple coatings is generally not economically feasible.
Accordingly one object of the invention to provide a novel Functionally Graded Material (FGM) having properties that can be altered at different locations in the tool or article without exhibiting failure at the interface between the different areas in the tool or article. This novel FGM is assembled of green sinterable powders, which may be plasticized powders, with common or compatible matrix and binder materials that enable designed interface transitional gradients and a bonding strength many times greater than in conventional laminar interfaces.
Another object of the invention is to provide an increase with respect to conventional wear laminates in the extremes of the wear, coefficient of friction, and toughness properties available at the working surfaces and cutting edges of the tool or article.
Yet another object of the invention is to provide a designed and engineered transition of properties rather than accepting natural or weaker interfaces. Still another object of the invention is to provide economy of manufacture by (a) reducing amounts of expensive materials needed, (b) using continuous extrusion, powdered injection molding (PIM), or calendering of plasticized powdered metals and ceramics, or dry powder layering of powdered metals and ceramics, and (c) reducing cost by reducing the number of process steps or process steps necessary to produce a tool or part.
These objectives are achieved by forming the tool or article from different types of the compacted and sintered material, such as the Tough-Coated Hard Powders (TCHP), disclosed in U.S. Pat. No. 6,372,346, which is herein incorporated by reference in its entirety. Such a material exhibits the combination of properties needed to provide superior metal cutting tools and articles. Because of the nature of the binder materials that bond the particles into the sintered article comprised of TCHP, the interface between the laminations is unusually strong. This strength is further enhanced by gradually transitioning the materials using extrusion or injection dies, rollers, or mold forms that provide unique grooves that interlock the different materials at their layered interfaces.